Telephone system



Oct. 20, 1925. x 1,557,992

- A.H DYSON TELEPHONE SYSTEM Filed June 4, 1906 9 Shets-Sheet 1 A. H. DYSON TELEPHONE SYSTEM 9 Sheets-Sheet 5 Filed June 4, 1906 Oct. '20, 1925. -:v

' A. H. DYSON TELEPHONE SYSTEM Filed June 4, 1906 9 Sheets-Sheet 4 Oct. 20, 1925, 1,557,992

' A. H. DYSON TELEPHONE SYSTEM Filed June 4, 1906 9 Sheets-Sheet 6 '9 Sheets-Sheet 7 Oct. 20,1925.

A.H.DYSON TELEPHONE SYSTEM Filed June 4, 1906 N N w #4 -Sm N M N N Q Q ;i I a ,a d v wW Mm w L MN Oct. 20, 1925.

A. H. DYSON TELEPHONE SYSTEM 9 Sheets-Sheet 8 Filed June 4, 1906 km MM miml lHu Oct. 20, 1925- A. H. DYSON TELEPHONE SYSTEM Filed June 4, 1906 9 Shets-Sheet 9 Patented Oct. 20, 1925.

- UNITED STATES PATENT OFFICE.

ALFRED H. DYSON, OF CHICAGO, ILLINOIS, ABSIGNOR, BY MESNE A SSIGNMIWTQ, TO.

KELLOGG SWITCHBOARD d: SUPPLY COMPANY, A CORPORATION OF ILLINOIS.

TELEPHONE swarm.

Application filed June 4, 1908. Serial No. 820,168.

To all whom z't-may concern:

Be it known that I ALFRED H. DYSON, a citizen of the United states, and resident of Chicago, county of Cook, and State of Illinois, have invented a new and useful Improvement in Telephone Systems, of which the following is a. specification.

The present invention relates generally to automatic telephone exchange systems and more particularly to that type in which electrically controlled switches are successivcly operated in response to current impulses transmitted over a callin line, to progressively connect a number 0 link-circuits so as to advance the circuit of the calling line to include a desired called line.

In systems of this class now in common use, each subscribers line is provided with a switch of relatively complicated construction, called a first selector, and these first selectors co-operate with similarly constructed second selectors and connectors in completin a connection between calling and called lines. On. the basis of ten per cent trunking, whichis that commonl employed, a ten thousand line exc ange equipped in this manner requires ten thousand first selectors one thousand second selectors and one thousand connectors. In order to reduce the cost of these systems, it has been proposed heretofore to replace the first selectors, which are individual to each line, by a simplified individual line switch in association with a reduced number of first selectors. Thus, on a ten per cent trunking, basis, a ten thousand line exchange equipped in this manner would require ten thousand'of these simplified individual switches, one thousand first selectors, one thousand second selectors and one thou= sand connectors.

The principal object of the present invention is to still further reduce the numbcr and cost of the interconnecting switches employed. To this end, I have devised a system in which switches individual to each line are done away with; and in their stead, the subscribers lines are arranged in groups and each group is provided with a plurality of switches which I term, line selectors? fewer in number than the number of lines in the group, and each group of line selectors is controlled by a simple switch mechanism common to the group. On the basis of ten per cent trunking, and assummg ten line selectors per group of one hundred subscribers lines, a system equipped in accordance with my invention requires one thousand line selectors, one hundred control or master switching mechanisms, one thousand first selectors, one thousand second seleetors and one thousand connectors.

Another object of my invention is to provide a system having a minimum number of relays and other parts and one which shall be efiicient in operation and economical to construct, install and maintain. It will, of course, be understood that in developing the invention along the lines indicated, I have provided features and circuit arrangements which are capable of use in other relations and that some of these are applicable to manual and so-ealled semi-automatic telephone systems, as well as to full automatic telephone systems.

The various features and aspects of the invention will be more fully understood upon-reference to the following detiled description taken in connection with the accompanying drawings, and the scope of the invention will be particularly pointed out in the appended claims.

Referring to said drawing, Fig. 1, which includes sheets 1, 2 and 3, is a diagram of a system constructed in accordance with my inVentiOn;Fig. 2 is a front elevation of the preferred master switch mechanism for the control of the line selectors; Fig. 3 is a side elevation of the same, the enclosing cover being shown in section; Fig. 4 is a partial sectional view of a line selector switch, illustratin in plan the primary magnet together with its associated mechanism, the section being taken on a plane indicated by the line 4- 4 of Fig. 9; Figs. 5 and 6 are detail views, illustrating the actuating magnets of certain switch mechanism associated with the first selectors; Fig. 7 is a detail of the off-normal switch associated with said line selector; Figs. 8, 9 and 10 are elevations of a line selector, each viewed from a difi'erent side; Figs. 11, 12 and 13 are similar views of a connector switch; Figs. 14, 15 and 16 illustrate modifications of that portion of the system shown in Sheet 1 of Fig- 1; Fig. 17 is a diagram of the line selector bank other modifications.

Referring in detail to the drawing and more particularly to the diagram of Fig. 1, A designates the substation equipment of two lines which terminate at the exchange in multiple contacts of connector and line selector switches. Connection is obtained between a calling and it called line through the agency of the master switch mechanism B, line selectors C, first selectors D, second selectors E, and connectors F. In practice, on a basis of ten thousand subscribers lines. ten per cent trunking, ten lineselector's C per group of one hundred lines and one control switch B per ten line selectors C, as previously indicated, there would be one thousand line selectors C, one hundred control switches B, one thousand first selectors D, one thousand second selectors E and one thousand connectors F. With this apportionment, each line would be multiplied to ten connectors and to ten line selectors, each connector to one hundred second selectors, each second selector to one hundred first selectors, and each first selector would be connected to one line selector. It is, of course, to be understood that these values may be changed to suit any required conditions, and that where an ultimate capacity of only one thousand lines is desired under the assumptions of trunking made, one set of selector switches may be omitted. In operation, the calling party removes his receiver and thereby, through the agency of the control switch mechanism B, sets an idleline selector switch G into operation to automatically seek out and establish connection with the calling line, thus extending the line circuit to a first selector D. The calling party then transmits impulses corresponding to the digits of the number of the subscriber wanted. The first of these operates the connected first selector switch D to pick out an idle second selector switch associated with the thousand group to which the called line belongs. The second set of impulses operates the second selector to pick out a connector associated with the hundred group to which the called line belongs. The third set of impulses operates the connector to pick out that group of ten contacts to which the called line helongs, and the final set of impulses causes the connector to pick out the called line contacts in this group.

The control switch mechanism B com prises a differential relay 26 which controls the circuit of a relay 32, which in turn controls the circuit of electromagnet 31 which is instrumental in stepping around the wiper 29 over its contacts 30.

The line selector switch C comprises the bank contacts 33, 35 and 37 with which the wipers 34, 36 and 38 co-operate in making connection between the link-circuit strands L L and the line limbs SP. These wipers are given both a primary movement and memos a secondary movement in response to the energizations and de-energizations of. the primig'iy magnet PM and the secondary magnet S respectively. By the primary movement, the wipers 34, 36 and 38 are stepped to a desired level or group of bank contacts; and by the secondary movement, they are moved over the contacts of the selected group until the desired contacts are encountered. The switch is also provided with a row of contacts 39, each of which corresponds to a level or group of bank contacts, and a wiper 41 co-operates with these in selecting the group in which the desired contacts are located. Normally, the contacts 33 and 39 are grounded; but as soon as a call is initiated,

the contacts 33 corresponding to the calling line, and the contacts 39 corresponding to the oup or level in which the contacts 33 of t e calling line are located, have their normal grounds removed. Thus in the operation of the switch, all the wipers are stepped around until the wiper 41 engages an ungrounded contact 39; then the secondary movement of the wipers 34, 36 and 38 takes place and is continued until the wiper 34 engages the ungrounded contact 33 of the calling line. The bank contacts 33, 35, 37 and 39 are connected to corresponding bank contacts of other selectors, one set of which is represented at 33", 35, 37 and 39.

The first and second selectors D and E and the connectors F are similar in construction and operation to the line selector, but are not provided with a wiper corresponding to the line selector wiper 41. In the operation of the first and second selectors, the impulses transmitted from the calling station step the wipers to the desired level or group and they are then automatically stepped over the contacts of said group until an idle linkcircuit is encountered. In the operation of the connector, the first set of impulses step the wipers to the desired level or group of contacts, and the second set moves them into engagement with the contacts of the desired called line.

tail, it will be observed that the removal of the receiver 1' from its switch-hook 1 at the substation of the calling party completes a bridge between the two line limbs l -S, through the transmitter 25 and the normally closed contacts 9 and 10 of the calling-device T. The completion of this bridge closes a circuit from the live pole of the battery B through the protective resistance 1*, normal contact 21 of the relay 20, line limb S, contacts 910, transmitter t, switch-hook 1, line limb P, normal contact 23 of relay 20, winding of the relay 14 to ground at'G. The closing of this circuit energizes the relay 14 sufliciently to attract its contacts 15, 16, 17 and 18. The movement of the contact 16 to its alternate position completes a circuit from the live pole of the battery B, through the winding of the relay 16", conductor 25 alternate contact 16 to ground at G, thereby energizing the relay 16 sufliciently to break the normal ground connection at G of all the multiple contacts 39 associated with that group including the calling line thereby es-' tablishing that condition whic will stop the wiper 41 of any one of the selecting switches C, which may be started, at the row of contacts which includes the contacts 33, 35 and 37 of the calling line. The movement of the contact 18 of the relay 14 to its alternate position removes the normal ground from the private contacts 33 associated with the calling line. This normal ground connection extends from the contacts 33, through the normal contact 24 and normal contact 18 to ound at G. The removal of the groun from the contacts 33 of the'callin line establishes that condition which wil cause the wipers 34, 36 and 38 to stop on the contacts of the calling line when they are engaged u on the secondary movement of the switc The movement of the contact 15 to its alternate position completes a circuit from the live pole of the battery B, through conductor 25, winding 28 of the differential relay 26 associated with the control switch B, through resistance 19, alternate contact 15 to ground at G. The closing of this circuit will energize the relay 26 sufiiciently to attract its armature and thus ground the wiper 29 of the control switchB. If at this time the wiper 29 is in engagement with a contact 30 leading to a line selector switch 0 which is in use, said wiper will be moved over its contacts until one connected with an idle line selector switchis encountered. Upon the first movement of the line selector switch, its switch contacts 49, 50 and 51 are moved to their alternate positions. Consequently, it the wiper 29 en ages a contact 30 leading to a busy line sel ector switch, a circuit will be completed from said grounded wiper, through the encountered contact 30 of said line selector, alternate contact 49, conductor 43, winding of relay 32 and conductor 25 to the live pole of the battery 13*. The closing of this circuit will energize the relay 32 sufficiently to attract its armature and thereby complete a circuitthrough the winding of the actuating relay 31 which is included in a vibratory circuit and, as indicated in Figs. 2 and 3, is arranged to step around the wiper 29 over its fixed contacts. So longas the wiper 29 engages a contact 30 connected with a busy line selector, a circuit through the winding of the relay 32 will be maintained; but as soon as the wiper 29 engages a contact leading to an idle line selector, the circuit of said relay 32 will be broken at the contact 49, and instead of said circuit, a circuit will be completed for the relay 45 of the idle line selector switch. This circuit, which includes the winding of the heat coil 65 and its normally closed contacts, extends through the winding of the relay 45, normal contact 49, contact 30, wiper 29 to ground. The relay 45 is thereby sufliciently energized to move its contacts 46, 47 and 48 into their alternate positions. The movement of the contact 48 to its alternate position completes a'vibratory circuit for the primary magnet PM which, by reason of its mechanical connections hereinafter referred to, steps the wipers 34, 36, 38 and 41 to that group or level in which the calling line contacts are located. During this movement the wi or 41 passes over the contacts 39. As in icated, the wiper 41 is normally out of engagement with the contacts 39, so that one primary step of the wipers is necessary to bring the wiper 41 into engagement with a contact 39. This same step, as previously indicated, causes the movement of the contacts 49, 50 and 51 to their alternate positions. The movement of. the latter contacts interrupts the initial energizing circuit of the relay 45 at the contact 49; but so long as the wiper 41 engages a grounded contact, an energizing circuit is maintained for the relay 45 from the live pole of the battery B, the winding of relay 45, contact 46, wiper 41, contact 39 to ground at G. However, if the contacts of the calling line are in the first group, the first encountered contact 39 will be ungrounded and, therefore, there will be no energizing circuit for the relay 45 and the contacts of the latter will return to their normal position, thereby interrupting the vibratory circuit of the primary magnet PM at contact 48 and stopping the further primary movement of the switch. If the contacts of the calling line are in other groups than the first, the wiper 41 will continue its movement over the contacts 39 until the ungrounded contact of the desired group is encountered, at which time the relay 45 will be de-energized and the primary movement of the switch discontinued, as just described.

The construction of the line selectors is such that, upon the first movement of the switch, not only are the contacts 49, 50 and 51 moved to their alternate positions, but the contact 53 is also moved to its alternate position. Thus, as soon as the relay 45 is de-energized after the selection of the group or level of contacts, an energizing circuit for the relay 54 is completed from the live pole of the battery B through the winding of said relay, normal contact 61, normal contact 47 and alternate contact 51 to ground at'G. The completion of this circuit suflllii ficiently energizes the relay 54 to move its contacts 55, 56, 57 and 58 to their alternate positions. The movement of the contact 57 to its alternate position completes a circuit from the live pole of the battery B through the Winding of the secondary magnet SM, contacts 57, 59, 60, and alternate contact 53 to ground at G. The magnet SM is included in a vibratory circuit and, by means of its mechanical connection hereinafter referred to, steps the wipers 31, 36 and 38 over the contacts 33, and 37 respectively, while leaving the wiper 41 unmoved.

By the movement of the contacts and 58 to their alternate positions, all battery and ground connections with the wipers 36 and 38 are removed, so that, as they pass over the contacts 35 and 37 of lines which may be in use, there will be no interference with conversation over said lines. Upon the first secondary movement of the switch parts, the construction is such that the switch contacts 61 and 62 are moved to their alternate positions. By this time, however, the wiper 34 will be in engagement with one of its contacts 33; and so long as it remains in engagement with a grounded contact, a maintaining circuit for the relay 54 will exist. This circuit extends from the live pole of the battery B, through the winding of said relay, alternate contact 56, wiper 34 to grounded contact 33. The connections between these contacts 33 and ground will depend upon the operative conditions of the subscribers lines to which they correspond. The contacts 33 of a called line will be grounded by way of alternate contact 24 and the contact 11 of the connector with which the called line is in connection. The contacts 33 of an idle line will be completed, as previously traced, through the normal contact 24 and normal contact 18 to ground at G The contacts 33 of a line, which is in use as a calling line, will be completed through the wiper 34 of the connected line selector C, conductor 34, normal contact 56 and winding of the release magnet RM to ground. As soon, however, as wiper 34 engages an ungrounded contact 33, which will be that of the calling line over which connection is desired, the circuit of the relay 54 will be interrupted and, by the return of the contact 57 to its normal position, the circuit of the secondary magnet SM will also be broken and the further secondary movement of the switch prevented. The wipers 34, 36 and 38 will thus be left in engagement with the contacts 33, 35 and 37 of the calling line, and the normal connection of the link-circuit strands L and L will be restored at the contacts 55 and 58. The engagement of the wiper 34 with an ungrounded contact 33 renders busy the private contacts 11 of the connectors associated with the calling line, energizes the relay 20 and (lo-energizes the relay The private contacts 11 are normally supplied with current from the live pole of the battery B through the winding of the relay 20; but upon the engagement of the wiper 34 with the contact. 33 associated with the calling line, these contacts 11 are connected to ground over a circuit including the alternate contact 18 of the relay 14, normal contact 24 of the relay 20, contact 33, wiper 34, conductor 34, normal contact 56 of relay 54, and winding of release magnet RM to ground. This sufficiently reduces the normal potential upon the contacts 11 to render them busy. By

this grounded connection, a circuit is also completed through the winding of the relay 20, and the latter is energized sufliciently to move its contacts 21, 22, 23 and 24 to their alternate positions, while the contacts of the release magnet RM remain unmoved, since said magnet will not operate through the resistance of the relay 20. By the movement of the contacts 21 and 23 to their alternate positions, the circuit of the line limbs S and P is continued so as to include the link-circuit strands L and L The movement of the contact 24 to its alternate position maintains a circuit for the relay 20. through the alternate contact 24, contact 33, Wiper 34, conductor 34, normal contact 56 and the winding of the release magnet RM to ground. In this operation, the alternate contact 24 is made before normal contact 21 is interrupted. The movement of the contact 23 to its alternate position interrupts the circuit of the relay 14 and allows the contacts of the latter to return to their normal positions. The movement of the contact 21 to its alternate position, in addition to continuing the line limb S, breaks the normal (fOlll'lPttlOll between the battery B and said limb. The interruption of the circuit of the relay 54 allows its contacts to return to normal, thereby extending the link-circuit strands L and L interrupting the circuit of the secondary magnet SM and thereby preventing further movement of the switch contacts while completing connection between conductor 34 and the winding of the release magnet RM. From this, it follows that the de-energization of the relay 54 must precede the energization of the relay 20 and the consequent de-energization of the relay 14.

In the operation above explained, it will be observed that as soon as the relay 14 is energized in response to the removal of the receiver from its hook at the calling station, a circuit will be completed through the winding 28 of the diiierential relay 26 and this will be sufficient to maintain the armature of said relay attracted until neutralized by a current flow through the other winding 27 of said' rclav. It will he observed that the latter-flow, however, will not occur until after an idle line selector switch C has been selected and it's wipers given their first step in a primary direction. As soon as this occurs, a circuit will be completed through the winding 27 of the relay 26, through conductor 44. alternate contact 50, resistance 52, normal contact 62, alternate contact 53 to ground at G". By a proper proportioning of the resistances l9 and'52, the current in the windings. 27 and 28 at this time neutralize each other, and the armature of said relay returns to its normal position. Thus the control switch B is free to continue its work of selecting other idle line selector switches for other calling lines without waiting for the complete connection of the first calling line with the desired called line. The winding 28 is common to the one hundred subscribers lines constituting the group to which the line selectors have access, and the winding 27 is common to such line sclectors. Therefore, if an additional call comes in before the contacts of the relay 26 have returned to normal, the current in the winding 28 will predominate over that in the winding 27 even after the resistance 52 has been included in circuit with the latter, by reason of the parallel paths to gro'und through the resistances 19 and 19' of the calling lines. Thus the armature of the relay 26 will be maintained attracted and, after setting one line selector switch in operation, the control switch B will be free to move its wiper into engagement with a contact leading to a second idle selector for the purpose of setting it in operation. H owever, as soon as connection has been completed by a line selector between the line limbs S and P and link-circuit strands L and L as previously noted, the relays 54 and 14 will be successively de-energized, thereby interrupting the paths through the winding 28 of the relay 26 and the resistance 1%) on the one hand, and the winding 27 of said relay and the resistance 52 on the other. .tt this point it may be noted that after the first secondary movement of the line selector by which the switch contacts 61 and 62 are moved to their alternate positions, the circuit through the winding 27 of the relay 26 and the resistance 52 is continued to ground at G, through the contacts 57 and of the relay 54, so that this branch is directly under the control of the relay 54 after the first secondary movement of the switch contacts. it should also be observed that upon the de-energization of the relay 14,

the circuit through the winding of the relay 16 is interrupted and, by its contacts, ground at (i is again placed upon the contact 39 of the group or level in which the QQfltaets of the callin line are located, thereby'leaving. the switches tree to select other 'de-energized so as to interrupt the circuit of the winding 28 of said relay 26, then the winding 27 would sufficiently energize the relay 26 to maintain its contacts closed, and

other line selector switches would be thereby set in operation. .Although this would not occur in the ordinary operation of the system by reason of the retarded return movement of the switch-hook 1, yet it might possibly be occasioned by the accidental crossing of the line limbs SP by a workman engaged in repairing the line, or otherwise. In order to prevent this operation of a number of line selectors, due to the momentary crossing of the line limbs, I rovide a locking circuit for the relay 14, w ich is maintaine during the time re uired by the line selector to pick out the cal ing line. This circuit is completed upon the energization of the relay 14 and extends from the live pole of the battery B, through the resistance 1'', normal contact 22 of the relay 20, alternate contact 17 of the relay 14, the winding of said rela to ground at G. This circuit is maintains as long as the relay 20 remains de-energized. As soon as said relay is energized, however, to complete the line limbs to the contactsv of the line selector, the locking circuit is interrupted at contact 22.

From the above description, it will be apparent that the terminals of any of the one undred subscribers in the group to'which a given line selector switch has access will be connected with a maximum number of twenty steps of the wi ers, while the average number of steps Wlll be more nearly in the-neighborhood of ten. As a speed of fifteen steps per second is very moderate for switches of the character I employ, and as a speed of thirty or more steps a second may readily be obtained, it will be obvious that there will be time for the desired operation of the master switch and line selector before the calling party begins to operate the disk 8 of his calling device T. If it is desired to employ slower switches, the subscribers may be instructed to pause an instant after removing their receivers before beginning to operate their calling apparatus, or any suitable means may be employed for giving the required time interval.

The next step in the calling operationconr sists in the manipulation of the disk 8 of the calling device T in accordance with the number of the telephone with which connection is desired. Thus, assuming that conversation is desired with. the substation at the right in Fig. 1, and that the number of the latters telephone is 3456, then the dial 8 will be manually rotated against the tension of its spring 8 four times, the first time bringing three of the teeth of the dial below the contact spring 5, the second time four, the third time five, and the fourth time six. Upon the return of the dial after its first movement, contact springs 4 and 5 will be engaged three times and this will be followed by a single engagement of the contact springs 6 and 7, since, in the normal position of the disk, one tooth lies below the spring 6. The three engagements of the springs 4 and 5 send three impulses of current over the 7 line limb P, while the single engagement of the springs 6 and 7 sends a single impulse over the line limb S. At the time these 1mpulses are being transmitted, the bridge through the transmitter t is interrupted at the contacts 9-10 which separate .when the dial is moved from its normal position. Three impulses transmitted over the line limb P energize and deenergize the primary relay 70, associated with the first selector switch D, three times, while the following single impulse over the line limb S energizes the secondary relay 77 once. A circult for the primary relay extends from the l ve pole of the battery-B through the winding of said relay, normal contact 7 3, normal contact 68, link-circuit strand L, wiper 36, contact 35, alternate contact 23, line limb P, spr1ngs 4- 5, to ground at G. The corresponding circuit for the secondary relay 77 extends from the live pole of the battery B through the winding of said relay, the normal contact 76, normal contact 74, link-circuit strand L Wiper 38, contact 37, alternate contact 21, line limb S, springs 6-7 to ground at G. Each impulse transmitted through the primary relay transmits correspondmg 1mpulses through the winding of the prlmary magnet PM of the first selector swltch D. This circuit may be traced from the live pole of the battery B through the winding of the magnet PM, normal contact 100 of the release magnet RM of said selector, normal contact 72 of the secondary off-normal switch 0 associated with the first selector D, and alternate contact 71 of the primary relay 70 to ground at G. The selector switch is so constructed that its wipers 101, 103 and 105 are given a primary movement in one direction, followed by a secondary movement at an angle thereto, as previously stated. By the primary movement, the wipers are brought opposite a level or group of bank contacts connected to corresponding second selector switches and, by its secondary movement, an idle second selector switch is selected. Thus in response to the three impulses transmitted from the primary relay 70, the primary magnet PM, through the agency of its associated mechanism hereinafter described, causes the, wipers 101, 10!. and 105 to he stepped to the third level or group of bank contacts, which are those assigned for connection to the third thousand group of subscribers lines. The following impulse transinitted over the line limb S, which energizes the secondary relay 77, closes a momentary circuit from ground at G, through alternate contact 78- of said relay, normal contact 79 of the off-normal switch 0, the winding of the private relay 80 to the live pole of the battery B thereby energizing said relay to move its contacts 81, 82, 83 and 84 to their alternate positions. By the first primary movement of the selector switch D, the contacts 85 and 86 are moved to their alternate positions' Consequently, as soon as the private magnet 80 is energized, current will flow over the vibratory circuit including the winding of the secondary magnet SM, alternate contact 81. alternate contact 86 and alternate contact 85 to ground at G". The magnet SM, by reason of its vibratory circuit and its mechanical connection with the wipers 101, 103- and 105, steps them over the co-operating bank contacts 102, 104 and 106. As soon as the circuit of the private relay 80 is interrupted,

its contactswill return to their normal positions and consequently the circuit of the secondary magnet SM is interrupted and the stepplng of the switch ceases. Therefore, while the wipers are passing over busy contacts, an energizing circuit for the magnet 80 is maintained. If an encountered contact 102 is that of a busy link-circuit. it will be connected to ground through one of itsmultiple contacts, through wiper 101 of another selector switch and over a circuit of said switch to ground as follows: through the normal contact 99, normal contact 81, alternate contact 86 and alternate contact 85 to ground at G. Therefore, as long as the wiper 101 of the selecting switch engages a grounded contact 102, the private relay 80 will be energized over a circuit from the live pole of the battery B through the winding of said relay, alternate contact 83, normal c0ntact 99, wiper 101 and contact 102 to ground. As soon, however, as an idle linkcircuit is encountered, this circuit will be interrupted and the further progress of the switch stayed, thus connecting the wipers 103105 of the link-circuit strands L-L'- to the contacts.104106 of the link-circuit including the strands L- connecting with an idle second selector switch E. At this point, it may be noted that the linkcircuit strands L'-L are interrupted at the switch contacts 6874; and that at the time the wipers 103105 are passing over the contacts 104106, the relay 80 is also encrgized and consequently all ground or battery connections with the wipers 103105 are I removed. This prevents interference with conversation through other selector switches over multiple contacts 104 and 106, over which the wipers 103 and 105 may pass.

The next step in the calling operation consists in movin the dial 8 far enough to bring four vteet 1 (corresponding to the hundreds digit in the number 3456) below the contact spring 5 and then allowing it to return to normal, thereby transmitting four impulses over the line limb P to actuate the primary relay four times. This, as before, will be followed by a single impulse over the line limb Sand will actuate the secondary relay 77. These impulses will cause the second selector switch E to move its wipers 120, 122 and 124 to the fourth level or group of subscribers lines, and thence into engagement with an idle link-circuit connecting with an idle connector switch F having access to the called subscribers line. The four energizations of the primary relay 70 cause four closures of the circuit from ground at G, through alternate contact 71 of said relay, the normal contact 82, wiper 103, contact 104, normal contact 107 of the secondary ofi' -normal switch 0 associated with the second selector switch E, normal contact 118 of the release magnet RM associated with said selector, the winding of the primary magnetPM to the live pole of the battery B. The impulses transmitted through the magnet PM are instrumental in producing the primary movements of the wipers 120, 122 and 124. The first movement from normal will move the contacts 114-115'- 116 to their alternate positions. The impulse transmitted by the secondary relay 77 will close a circuit from ground at G", through alternate contact 78, normal contact 84, wiper 105, contact 106, normal contact 108 of the secondary off-normal switch 0 winding of the private relay 109 of the sec ond selector switch E to the live pole of the battery B, thereby energizing said relay and causing it to disconnect wipers 122--124 from circuit by moving the contacts110113 to their alternate positions, while at the same time movin g contacts 111112 to their alternate positions. The energization of the private relay 109 thus completes a circuit for the secondary magnet 8M by which the wipers 120, 122 and 124 are given their secondary movement. This circuit extends from the live pole of the battery B, through the winding of said secondary magnet SM alternate contact 111, alternate contact. 116,

. and alternate contact 114 to ground at G.

scription of the first selector switch D, when an idle link-circuit is encountered. At this time,as previously indicated, wipers 122-124 are again included in circuit upon the return of the contacts 110-113 to normal, thus projecting the circuit of the calling line through the line selector switch C of said line and the selector switches D and E. It will be noted that as the wipers 122-124 are passing over the contacts 123125, they are disconnected from battery or ground, thus preventing interference with possible conversation being held through other selector switches, over-whose multiple contacts these wipers pass.

The next step in the calling operation consists in moving the dial 8 into a position to transmit five impulses over the line limb P, through the primary relay 70, followed by a single impulse over the line limb S, through the secondary relay 77. The primary impulses are extended from the primary relay over a circuit extending from ground G at said relay, through wiper 103 of the first selector switch D as previously traced, thence through contact 104, normal contact 110, wiper 122, contact 123, normal contact 126 of the secondary off-normal swltch of the connector F, normal con tact 128 of the release magnet RM of said H connector, through the winding of the primary magnet PM to the live pole of the battery B In this instance, the five impulses of current transmitted through the primary magnet will step the wipers 154, 155 and 156 to the fifth level or group of contacts to which the subscribers lines, having numbers from 3450 to 3459 inclusive, are connected. At the ,first movement of the switch in response to these primary impulses, the switch contact 157 is moved to its alternate position, thereby grounding the associated bank contacts 121 through the winding of the release magnet RM The secondary impulse following these primary impulses closes a circuit from ground G at the secondary relay 77 to the wiper 105 of the first selector switch D as previously' traced, thence through contact 106, normal contact 113, wiper 124, contact 125, normal contact 131, normal contact 130, winding of the secondary magnet SM to the live pole of the battery B. This causes a momentary energization of the secondary magnet SM which is instrumental in giving the wipers one step in their secondary direction. As indicated in Figs. 11, 12 and 13, the wipers of the connectorvare normally two steps distant from the first set of bank contacts and consequently this single step does not bring them into engagement, but is occasioned for the purpose of actuating the secondary offnormal switch contacts 126-131. At this time, the contact 126 is moved to its alternate position; and at the same time, the con tact 131 is moved far enough to break its normal contact, but not far enough to close its alternate contact. The movement of the contact 131, far enough to make its alternate. contact, does not occur until the next step of the switch. The pur ose of this operation is to prevent the a ve secondary impulse from hanging over and being transmitted through the right-hand winding of the busy relay 137 by Way of the normal contact 136, which might occur if the contact 131 were thrown at once to its alternate position.

The next step in the calling operation consists in moving the dial 8 so as to transmit six primary impulses, again followed by a single secondary impulse. In this case the circuit under control of the primary relay 70 is the same as that heretofore traced as far as contact 123. From this point, it extends through alternate contact 126 of the secondary off-normal switch 0 normal contact 133, normal contact 130 of the release magnetltM, through the winding of the secondary magnet 8M to the live pole of the'battery B Thus the secondary magnet is energized and dc-energized six times, thereby stepping the wipers 154, 155 and 156 into engagement with the sixth set of contacts 11, 12 and 13 in the fifth level or group, thus establishing connection with the secondary relay 77 to the contact 125 of the tion.

second selector switch E, over a path the sameurs that heretofore traced. From this point, its clrcuit is continued through alternate contact 131 of the secondary off-normal switch 0 normal contact 136 of the control relay 1.32, the right-hand winding of the relay 137 which controls the application of the busy signal, to the live pole of the battery B The completion of this circuit momentarily energizes the relay 137 to cause it to move its contact 138 to its alternate posi- In case the desired line is in use, we have seen that its private contacts 11 will befconnected to ground through the winding of the release magnet RM of the line selector switch with which connection has been established, if the desired line has been operated as a calling line. On the other hand, if connection has been established with the desired line as a called line, the private contacts 11 will be grounded through the wiper'154 of another connector switch apply the busy signal.

F, contacts 139-140, which will be in engagement at this time, through the winding of relay 132 to ground at G. Conse-. uently, if the called line is busy, a path or current will be completed so as to lock the relay 137 and thereby apply busy current to the line to signal the calling party. This circuit may be traced from the live pole of the battery B through the right-hand winding of the relay 137, normal contact 139, Wiper 154 and contact 11 to ground over either of the paths previously traced. The windings of the relay 137 are so arranged that at this time their effects will be cumulative and consequently the contact 138 of the relay will be held closed. 'The busy signal may be applied to the line in any preferred manner; and in the present in stance, I have illustrated for this purpose an interrupter 151, included in a primary circuit with one winding of an induction coil 1, and battery and by the other winding of said coil inductively with condenser 0, relay contact 138, normal contact 136 of the control relay 132, the alternate contact 131 of the secondary off-normal switch, second selector switch contacts 124r125, normal contact 113, first selector switch contacts 105106, normal contact 84, condenser 0,

normal contact 58, line selector switch contacts 3738, alternate contact 21 of the relay 20, line limb S, contacts 9-10 of the calling device T, transmitter t, switch-hook 1, line limb P, alternate contact 23 of relay 20, line selector switch contacts -36, normal contact of the relay 54, normal contact 68, normal contact 73, winding of the primary relay 70, and battery B to ground. The "current induced in this secondary circuit will produce the customary buzzing sound in the receiver ofthe calling party, as an indication to him that the called line is busy.

In case the called line is not busy, the final secondary impulse transmitted from the calling station will only momentarily energize the relay 137 and will, therefore, not

Upon the de-energization of this relay, its mechanical construction is such, as will hereinafter more fully appear, as to cause a movement of the contact 139 to its alternate position, thereby placing ground on the multiple contacts 11 of the called line over the previously traced path from the wiper 154, through contacts 139- 140, winding of the control relay 132 to ground at G. The placing ofv ground upon the contacts 11 over this path com- 'pletes an energizing circuit for the relay 20 associated with the called line. This circuit extends from the live pole of the battery B",

\ former, the contacts 21 and 23 are moved to their alternate positions to complete the connection between the line limbs S and l and thecontacts 12 and 13, while at the same time interrupting the circuit through the relay 14 so as to prevent the initiation of a call over said line. The energization of the relay 132 interrupts the circuit of the secondary magnet SM at the contact 133 and completes the strands L and L ofthe link-circuit at this point. At the same time. the engagement of the contacts 133-134 completes a circuit from ground G", through the normal contact of relay 142, normal contact 129, contacts 134-133, linkcircuit strand L, alternate contact 126 of the secondary off-normal switch 0*, second selector switch contacts 123-122, normal contact 110, first selectorswitch contacts 104-103, normal contact 82, normal contact 71 of the private relay 70, normal contact 69, winding of relay 89 to the live pole of the battery B The completion of this circuit energizes relay 89 sufficiently to move its contacts 73-76 to their alternate positions and thereby complete a circuit for transmission current to the calling substation from the live ole of said battery, through the lower win ings of the relays 90-91, alternate contact 76, normal contact 74, linkcircuit strand" L line selector contacts 37-38, line limb S, through the transmitter at the substation, line limb P, lineselector contacts 35-36, link-circuit strand L, normal contact 68,'alternate contact 73, upper windings of the relays 91-90 to groundat G 1 The arrangement of the windings of the relay 91 is such that at this time their effects are cumulative and consequently the relay is energized to attract its contacts 92-93 and thereby complete an additional path to the link-circuit strands L and L from the live pole of the battery B through the lower windings of the relays 90-91, closed contact 92, normal contact 98, to the link-circuit strand L and from the linkcircuit strand L, through normal contact 97, closed contact 93, the upper windings of the relays 91 and 90 to ground at G The arrangement of the windings on the relay 90 is such that their effects are ditlerential and consequently the contact of this relay is'not closed at this time. At the same time that the control relay 132, associated with the connector F, is energized, a circuit is completed through the winding of the ringing relay 148. This circuit extends from the live pole of the battery B through the winding of said relay, normal contact 145, contacts 141, 139 and 140, through the winding of the relay 132 to ground at G. The ringing relay 148 is thereby energized closing its contacts 149-150 and thereby completing a circuitover whichringing current is supplied to the called line. The path formittently transmitted from the generator 153 and, .during the non-transmitting intervals, the circu1t is grounded at G.- The relay 143 is so constructed that the passage of ringing current through its winding in circuit with thecondenser a will not move its contacts from their normal positions. As soon as the calledparty removes his receiver from its hook, thereby completing a conductive brid e between the line limbs S and P through is transmitter, battery current is transmitted over the ringing circuit just traced, except that through the substation it finds a path through the closed bridge including the transmitter. The battery current over this circuit now energizes the relay 143 to cause the movement of its contacts 144, 146 and 147 to their alternate positions, thereby completing the adjacent portions of the link-circuit strands L and L atthe contacts 146-147, interrupting the circuit through the ringing relay 148 at contact 145 and closing a locking circuit through the upper winding of the relay 143 at the contacts 144-145. This locking circuit extends from the live pole of the battery B, through the upper winding of the relay 143, contacts 144-145, contacts 141, 139 and 140, and winding of relay 132 to ground at G. The breaking of the ringing relay circuit discontinues the application of ringing current to the called line, and the closing of the contacts 146-147 completes a new path for transmission current from the live pole of the battery B, through the upper winding of the relay 142, link-circuit strand L, wiper 155, contact 12, line limb P, through the transmitter at the substation, line limb S, contact 13, wiper 156, link-circuit strand L, and the lower winding of the relay 142 to ground at G. The closing of this circuit energizes the'relay 142 to open its contacts and thereby open the circuit of the relay 89 associated with the first selector switch D, thereby deenergizing said relay. The mechanical associations of the relay 89 are such that upon its'de-energization the switch contacts 68-69 and 74-75 are thrown to their alternate positions, thereby making the last connection necessary to the completion of the talking circuit between the calling and called stations. At the same time, the contact 75 is groundedat Gr and a circuit is thereby completed through the winding of the relay 94, which is energized sutficiently to move its contacts 95-496 into engagement with the contacts 97- 98 respectively and at the same time causing the latter to break their normal contacts. By this means, the direction of current flow to the calling station is reversed. This is occasioned for the purpose of operating paystation and other devices which may be used in the system.

In order to restore the parts to normal position at the end of conversation, it is only necessary for either or both parties to hang up their receivers. Associated with each switch-hook, is a contact 3, over which a projection 2 on the switch-hook passes when the receiver is taken down. U on the return of the receiver, the projectlon 2 moves the spring to its alternate contacting position to ground both sides of the line. By the time the switch-hook reaches its normal position, the projection 2 has passed over the spring 3 and the parts are left in their normal ositions. If the calling party first restores is receiver'to the switch-hook and thereby grounds both line limbs, the normal balance of the relay 90 is destroyed, since a circuit is now completed through the lower winding of said relay over one line limb to ground at the substation. The relay thereu on closes its contacts and a circuit is comp eted from the live pole of the battery B through the release magnet RM of the first selector switch D and the release magnet RM of the line selector switch 0. This circuit may be traced from the live pole of the battery B", through the winding of the release ma net RM, closed contacts of the relay 90 an windin of the release magnet RM to ground. Tie energization of release magnet RM' closes a second circuit through the release ma net RM of the second selector switch. T is circuit extends from the live pole of the battery B through the resistance r alternate contact 99, wi er 101, contact 102, alternate contact 115, winding of the release ma et RM to ground at G". The energizatlon of release magnet RM in turn closes a circuit through the release magnet RM of the connector switch Fl The circuit of this latter magnet extends from the live pole of the battery B, through the resistance 1", alternate contact 117, wiper 120, contact 121, alternate contact 157 and winding of the release ma net RM. to ground at G". The construction of the substation equipment is such that the ground on the line limbs will remain long enough to permit these release relays to be energized. Upon the deenergization of each of these relays, the associated switch .parts are returned to normal. This is due to the mechanical construction and arrangement of the parts, as will be hereinafter more fully pointed out.

If the called party first hangs .up his receiver, he will similarly ground both line limbs, but this will not be instrumental in releasing the switch mechanism, since at this time a circuit will be completed throu h the upper winding of relay 142, over t 0 line limb P to the ground at the substation. This circuit will maintain the relay- 142 cuergiz'ed to hold its contacts open the same as during conversation. However, as soon as the switch-hook reaches its normal position and the ground is removed, and the bridge for battery current between the line limbs S and P interru ted, the relay 142 will be de-energized an will thereupon, by the closing of its contacts, complete a circuit from ground at G, through normal contact 129, contacts 134-133, link-circuit strand L, alternate contact 126, contacts 123122, contact 110, contacts 104103, alternate contact 68, contacts 97-95, closed contact 92, the lower windings of the relays 91-90 to the live pole of the battery B The closing of this circuit will destroy the normal balance of the windings of the relay 90 and will energize it sufficiently to close its contacts with the consequent releasing of the difi'erent switching mechanisms, as previousl pointed out.

The energization of the release ma net RM associated with the line selector switch causes the return of the switch contact 53 to its normal position, thereby completing a circuit from the live pole of the battery B, through the winding of the relay 54, alternate contact 61 and normal contact 53 to ground at G. The completion of this circuit energizes the relay 54 to interru t the link-circuit strands L and L at t e contacts 5558, thereby removing all ground or battery connections from the wipers 36 and 38. The energization of the release magnet RM, by closing its contacts 63 and 64, shunts the open contacts 55 and 58 and thereby maintains the unbalancing circuit of the differential rela 90. Upon the tie-energization of the re ease magnet RM, the wipers 34, 36, 38 and 41 return to normal. During this movement, the contacts 49, 50, 51, 61 and 62 are also returned to normal. It should be noted that during this return movement of the wipers, interference with conversation over other linkcircuits is prevented, since at this time the wipers 36 and 38 are free from battery and ground connections, the contacts 63 and 64 of the release magnet having returned to normal, and the contacts 55 and 58 of the private magnet 54 being attracted until the return of the contact 61 to normal, which occurs at the instant of the movement of the line selector switch wipers 34, 36 and 38 out of engagement with the last bank contacts 33, 35 and 37.

Similarly, upon the energization of the energized to move its contacts 82 84 out of, connection with the link-circult strands L'Ifi. This circuit is maintained until the contact 85 is returned to its normalposition, which occurs only when all the arts have reached their normal positions. pon the de-energization of the release magnet RM, its mechanical connections are such that the wipers return to normal, and -upon such de-energization, the contacts 68, 69, 74 and also return to normal. From this it will be seen that as the wipers 103 and 105 pass over the contacts 104 and 106 of bus selector switches, there will be no inter erence with conversation.

Similarly, upon the energization of the release ma net RM of the second selector switch E, t e switch contact 116 will be returned to normal, thereby completing a circuit through the private relay 109 from the live pole of the battery B, through the winding of said relay, normal contact 116 and alternate contact 114 to ground at G. This circuit is maintained until the wipers reach their normal positions, at which time the contact 114 returns to normal, thereby interrupting the circuit. As soon as the circuit is completed, the relay 109 is energized and the link-circuit strands L and L are interrupted at contacts 110113. In order to maintain the circuit for the magnet 90 from the called station, the contact 110 is bridged by the contact 119 which is closed upon the energization of the release magnet R-M Upon the de-energization of the release magnet, the contact 119 is opened and thewipeis 122-124, which are then free to return to normal, are free from ground and battery connections and, therefore, there will be no interference with conversation through other selector switches. Upon the energization of release magnet RM" associated with the connector switch 1 the circuit from ground G through the lower winding of the differential magnet 90, is interrupted at contact 129. At this time. all the release magnets RM, RM, RM and RM are caused to be de-encrgized. The de-energization of the release magnet RM, as in the other cases, is instrumental in returning the parts of the connector switch F to normal. This magnet is also related to the contact 139 so that, upon the energization of the magnet, said contact is returned to its normal position, thereby breaking the locking circuit through the relay 143, as well as the circuits throu h the control relay 132 and relay 20. The e-energization of relay 14-3 breaks all ground and battery connections to the wipers 155156 so that,.as they pass over the contacts 11-12 of other lines,

7 as before described.

there will be no interference with possible conversation thereover. The de-energization of the relay 20 restores the normal connections of the line limbs 8-1 of the called line, while the de-energization of the control relay 132 breaks the link-circuit strands If and U at contacts 133' and 136 and also interrupts the circuit from ground G through the differential relay 90 by which the operation of the release magnets of the several switches is controlled.

If the calling partys line has been projected beyond the line selector, and the callmg party hangs up his receiver before obta-min connection with the called line, he will simultaneously energize both the primary and secondary relays 70 and 77 over circuits to the substations such as have been previously traced, except that at the substation the ground connection will occur at G instead of G. \Vhen both the primary relay 70 and the secondary relay 77 are s1- multaneously energized, a circuit is completed from the live pole of the battery 13 through the windin of the release magnet RM of the first seector switch D, thence through the contacts 87 and 88 of the pri mary and secondary relays and winding of the release magnet RM to ground, thereby momentarily energizing both release magnets RM and RM and causing them to release their switches and allow them to return to normal, as before described. In

,the event of either the second selector or the second selector and theconnector being partiallyoperated, the release magnets RM and RM will be energized and (lo-energized In order that an impulse may not be improperly sent through the primary magnet PM ofthe first selector switch D, it the calling party should take off his receiver and immediately return the 'same, allowing only sufiicient time for the contacts 87 and 88 to come into engagement, the contact 100 controlled by the. release magnet RM is provided. Upon the engagement of the contacts 87 and 88. both contacts 71 and 78 are grounded at G and since the contacts 72 and 79 of the. secondary oil-normal switch 0 are moved to the alternate position only upon the first secondary movement of the switch, a circuit would thus be completed through the primary magnet PM, if it were not for the contact 100 which is opened by the energization of the release n'lagnet RM upon the engagement of the contacts 87 and 88.

In the system, I have shown a protective device in association with the line selector and have arranged its contacts so that. when the device is operated, the conductor 43 and the conductor running to the contact. 30 of the master switch B are connected, as clearly illustrated in Fig. 1. As will be apparent from the previous descriptiom'this will ren-' 

